Fibrous products and methods of manufacture

ABSTRACT

Fibrous materials made from multiple populations of fibers, and compositions related to preparing such, are disclosed. In some instances, fiber populations can have different native surfaces, in which at least one of the populations can be surface modified, for example by the use of a polycation (e.g., a polyamine), secondary polymers, complementary polymers, and/or other agents. These populations can be combined to form a fibrous composition, where the surface treatments can enhance properties of the end product. Populations of fibers can also have other physically varying characteristics (e.g., shapes and sizes). Such compositions can be utilized in a variety of applications such as paper products, filters, fire-retardant fibrous products, protein adsorbing fibrous materials, and fibrous sheets having conducting properties. Methods of preparing portions or the entirety of such fibrous materials are also disclosed.

RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/US2009/057769, which designated the United States and was filed on Sep. 22, 2009, published in English, which claims the benefit of U.S. Provisional Application No. 61/098,907, filed on Sep. 22, 2008. The entire teachings of the above applications are incorporated herein by reference.

FIELD OF THE APPLICATION

This application relates generally to fibrous products formed from two or more fiber populations.

BACKGROUND

Fibrous products containing cellulose by itself or mixed with other fibers have many useful applications. Among consumer applications, fibrous products such as paper towels are used to dry or wet clean, absorb aqueous liquids etc. Fibrous products have other uses for consumers and for industry, for example as filters, fabrics, and specialized materials having, for example, conductivity, fire resistance, and the like.

Cellulose fibers in wood pulp and other natural fibers used to make fibrous products are typically hydrophilic, and can have limited strength and chemical resistance. These properties can limit their use to milder environments and can limit the reusability of such products, Synthetic fibers may have advantages for use in fibrous products. Synthetic fibers are often hydrophobic. They typically have good chemical resistance, and may have good dry and wet strength, depending on their chemical structure. Synthetic fibers are also typically expensive. Moreover, to the extent that a synthetic fiber is fossil-fuel based, its use can have a significant environmental impact. As they are fossil fuel based, the environmental impact of using a fibrous product completely made of such synthetic fibers is high. In light of these issues, a method is needed where two populations of fibers, each having desirable characteristics, could be intimately combined to produce fibrous products.

Many disposable, absorbent products, especially hydrophilic ones, comprise randomly arranged webs of relatively low-density fibrous materials such as cellulose fibers. The random web may be produced by techniques known in the art such as wet laying, air laying or solvent laying of the fibers. The technique of wet laying involves the slurrying of the fibers in water; when the water is drawn off, the web dries into a final product. With wet laying, the soft and pliable fibers are attracted to each other by hydrogen bonding, and they sag against each other to create a denser product than that formed by air laying or solvent laying. The denser product formed by wet laying may be to stronger, but it may also be less absorbent. Wet strength additives that are employed during manufacture may render the product more hydrophobic.

Adding hydrophobic fibers to a hydrophilic fibrous web may adversely affect the wicking properties and absorption capacity of the web. For example, fibrous webs with large proportions of uniformly distributed microfibers among the larger fibers (e.g., cellulose) generally have less integrity because the microfiber component provides less strength than the larger fiber component, a limitation that is particularly apparent during applications requiring wet strength. In addition, microfibers may become detached from the fibrous web and form a particulate deposit on the surface being cleaned, like lint, fuzz, or dust.

Nonwoven products may use mechanical means for dispersing their component fibers before coalescing them into a useful product. Manufacturing processes may produce staple non-wovens, where larger fibers between ¼″ and 1½″ may be used either alone or in combination with other fibers or fiber blends using a wetlaid process or a carding process. Manufacturing processes may also produce spunlaid non-wovens, where fibers are spun then directly dispersed into a web by deflectors or by air streams.

Other manufacturing methods will be familiar to skilled artisans, such as wet-laid mat processes or flame-attenuated mat processes. Typically, nonwoven processes employ a bonding step to impart mechanical strength.

Non-woven webs have many end-uses, including formation of filtration media. Air-laid and wet-laid processes can be used. When used for the filtration of fluid streams and removal of particulate matter therefrom, filtration media can be adversely affected by incorrect pore size, reduced efficiency, reduced permeability, lack of strength, or other problems arising from the nature of the non-woven web. A need exists in the art, therefore, for a fibrous web suitable for filtering a variety of fluid streams, for example gaseous streams such as air, and aqueous and non-aqueous liquids, including water, wastewater, oil and the like. Desirably, such a fibrous web can possess properties that achieve appropriate permeability for removing designated particulate matter, substantial filtration efficiency, high wet strength, and long filtration life.

Furthermore, a need exists in the art for fibrous products that are absorbent, strong, and abrasion-resistant. A need further exists for techniques that can easily incorporate disparate or similar populations of fibers or microfibers into a fibrous sheet under a variety of manufacturing conditions to form a variety of products.

SUMMARY

Disclosed herein are embodiments of fibrous compositions of mixed fibers that include a first population of fibers, and a second population of fibers having native surface characteristics differing from native surface characteristics of the first population of fibers, at least one population of fibers being surface modified by a polycation, the first and second population of fibers being mixed together in the form of a porous composition. The fibrous composition can include a sheet structure. The fibrous composition can further comprising a wet strength component. The wet strength component can comprise at least one of a melamine-formaldehyde resin, a urea-formaldehyde resin, and an epoxidized polyamine-polyamide resin. In embodiments, the polycation can comprise a polyamine, and the polycation can be bound to at least one fiber using a coupling agent. In embodiments, the polycations can comprise chitosan analogues such as polycations (e.g., polyamines) modified with one or more types of hydrophobic side groups. In embodiments, the polycation couples at least two fibers together. In embodiments, at least one population of surface-modified fibers is attached to the polycation by at least one of electrostatic interactions, covalent bonding, hydrogen bonding and hydrophobic interactions.

In embodiments, the surface-modified population of fibers can comprise synthetic fibers. In embodiments, at least one surface-modified population of fibers can comprise fibers exhibiting a native hydrophobic surface. The native hydrophobic surface can be surface modified to a hydrophilic surface. In embodiments, at least one population of fibers in the composition can comprise natural fibers. In embodiments, at least one population of fibers can comprise at least one of microfibers and larger fibers. In embodiments, at least one population of fibers can comprise fibers having dissimilar sizes.

In embodiments, at least one surface modified population of fibers comprises a polysaccharide coupled to at least one of the fibers. In embodiments, at least one surface modified population of fibers comprises synthetic fibers having a cellulose-based material coupled thereto. Such compositions can further comprise a crosslinker for coupling the surface modification to at least one of a fiber and another portion of the surface modification.

In embodiments, the composition can further comprise a complementary polymer capable of attractively interacting with the polycation. The complimentary polymer can comprise at least one a pectin, xanthan gum, carboxymethyl cellulose, polyacrylic acid, polymethacrylic acid, polyacrylamide, polyethylene glycol, polymers derived from maleic anhydride, and copolymer having at least one segment comprising any of the aforementioned polymers. In embodiments, the complementary polymer can comprise at least one of an epoxide, an anhydride, a carboxylic acid, and an isocyanate.

In embodiments, the composition can comprise at least one population of fibers comprising a fire-retardant material, an electrically conductive material, or a nanofibrillated cellulose-based material. In embodiments, the composition can comprise at least one surface-modified population of fibers that exhibits protein adsorption resistance relative to a native surface of the surface modified population of fibers. In embodiments, the composition can form at least a portion of a filter paper.

Disclosed herein are methods for forming a mixed fiber composition, comprising attaching polycations to a first population of fibers; providing a second population of fibers having native surface characteristics differing from native surface characteristics of the first population of fibers; forming a precursor fiber composition comprising the first population of fibers and the second population of fibers; and creating a sheet structure from the precursor fiber composition. In practices of the methods, the step of attaching polycations can comprise precipitating the polycations onto the first population of fibers. The step of attaching poycations can comprise attaching a coupling agent to the polycations.

Certain practices of these methods can comprise adding a wet strength component to the fiber composition. The step of adding the wet strength component can take place after mixing the first population of fibers and the second population of fibers together. These methods can further comprise adding a complementary polymer having an anionic portion to the first population of fibers; and attaching the complementary polymer to the at least one of the polycations. According to certain practices of these methods, at least one population of fibers comprises synthetic fibers and at least one population of fibers comprises natural fibers.

DESCRIPTION

As used herein, the term “fibrous structure” or “fibrous web” refers to any arrangement of individual fibers or filaments that are interlaid with one another. In some embodiments, the fibrous structure or web has a nonwoven character. In some embodiments, the fibers or filaments form a disorganized pattern (e.g., a substantially random formation or structure whose organization has little discernable pattern). Some techniques for fabricating fibrous structures are known in the art, including papermaking techniques and techniques for making nonwoven materials.

As used herein, the term “composite material” refers to a material comprising two populations of fibers.

As used herein, the term “fiber” refers to an entity which possesses a large aspect ratio (e.g., a dimensional length much larger than its cross-sectional dimension (e.g., a diameter)). For instance, in embodiments, the aspect ratio of the fibers can be larger than about 10, 20, 30, 50, or 100.

As used herein, the term “microfiber” refers to synthetic or natural fiber having a smaller cross-sectional width and/or total length relative to a “larger fiber,” as utilized in the present application. In some embodiments, the microfibers have an average cross sectional width (e.g., diameter) of no more than about 100 microns. In embodiments, a microfiber may have an average cross sectional width between 0.5 and 50 microns. In other embodiments, a microfiber may have an average cross sectional width between 4 and 40 microns. In embodiments, a microfiber may have an average cross sectional width less than 30 microns. The size of the microfibers can also be characterized in terms of denier units. In some embodiments, the microfibers, on average, are less than about 10 denier, or less than about 5 denier, or less than about 2 denier, or less than about 1 denier.

In some embodiments, the ratio of the average cross-section dimensions (e.g., diameters) of the larger fibers to the microfibers can be greater than about 5, 10, 20, 50, 100, 500, 1000, 5000, or 10000.

In embodiments, microfibers may be initially dispersed in an aqueous or solvent medium in a range of concentrations, for example ranging from solutions in which the fibers are barely wetted with the medium to solutions where the fibers are substantially diluted by the medium.

In particular instances, at least some of the microfibers can include a fiber having a plurality of fibrils (i.e., a fibrillated fiber), which can potentially be separated. A fibrillated fiber can be produced from a fiber during fiber processing, where a precursor fiber is abraded or otherwise mechanically distressed. For example, processes (e.g., papermaking) can increase the internal and external fibrillation of a cellulosic pulp. A fibrillated fiber can include portions having a cross sectional width less than about 100 microns, though the unfibrillated fiber may have a cross sectional width larger than about 100 microns. Fibrils can have a nanofiber structure, e.g., exhibiting an average cross sectional width between about 1 nm and 1 micrometer, or between about 50 nm and about 500 nm. In some embodiments, the microfibers are embodied as nanofibers, which can originate from fibrils of a microfiber.

Fibrillated fibers can be advantageously utilized in some embodiments of the present invention. In general, the greater the fiber surface area available for contact within the pulp, the greater the extent of cellulose-to-cellulose hydrogen bonding between the fibers. This fiber-fiber bonding occurs, for example, when water is removed from a pulp during wet pressing and drying in papermaking. The presence of fibrillations can enhance the strength of a fibrous product because the fibrils increase the fibers' surface area and thus the potential for greater hydrogen bonding. In addition to potentially improving the inter fiber bonding, the fibrillation also provides additional surface area for retaining additives such as surface modifications.

As used herein, the term “larger fiber” refers to any synthetic or natural fiber that is longer and/or broader (i.e., having a larger cross sectional length) than a microfiber. In some embodiments, larger fibers have a cross-sectional length (e.g., diameter) of 3-50 microns, 7-70 microns, or 150-600 microns, when used with smaller microfibers. One example of larger fibers is the cellulosic fiber associated with typical wood pulp formulations.

As used herein, the term “population” refers to a collection of fibers or microfibers wherein all the fibers or microfibers are the same. The fiber type in the fiber population can be of any kind: e.g., synthetic, artificial or natural fibers, larger fibers or microfibers.

As used herein, the term “synthetic fibers” include fibers or microfibers that are manufactured in whole or in part. Synthetic fibers include artificial fibers, where a natural precursor material is modified to form a fiber. For example, cellulose (derived from natural materials) can be formed into an artificial fiber such as Rayon or Lyocell. Cellulose can also be modified to produce cellulose acetate fibers. These artificial fibers are examples of synthetic fibers.

Synthetic fibers can be formed from synthetic materials that are inorganic or organic. Synthetic inorganic fibers include mineral-based fibers such as glass fibers and metallic fibers. Glass fibers include fiberglass and various optical fibers. Metallic fibers can be deposited from brittle metals like nickel, aluminum or iron, or can be drawn or extruded from ductile metals like copper and precious metals. Organic fibers include carbon fibers and polymeric fibers. Examples of polymeric fibers include fibers made from polyamide nylon, PET or PBT polyester, polyesters, phenol-formaldehyde (PF), polyvinyl alcohol, polyvinyl chloride, polyolefins, acrylics, aromatics, polyurethanes, elastomers, and the like. A synthetic fiber may be formed from more than one natural or synthetic fiber. For example, a synthetic fiber can be a coextruded fiber, with two or more polymers forming the fiber coaxially or collinearly. In general, synthetic fibers can be manufactured in any number of manners, including those known to one skilled in the art (e.g., solution spinning).

As used herein, the term “natural fiber” refers to a fiber or a microfiber derived from a natural source without artificial modification. Natural fibers include vegetable-derived fibers, animal-derived fibers and mineral-derived fibers.

Vegetable-derived fibers can be predominately cellulosic, e.g., cotton, jute, flax, hemp, sisal, ramie, and the like. Vegetable-derived fibers can include fibers derived from seeds or seed cases, such as cotton or kapok. Vegetable-derived fibers can include fibers derived from leaves, such as sisal and agave. Vegetable-derived fibers can include fibers derived from the skin or bast surrounding the stem of a plant, such as flax, jute, kenaf, hemp, ramie, rattan, soybean fibers, vine fibers, jute, kenaf, industrial hemp, ramie, rattan, soybean fiber, and banana fibers. Vegetable-derived fibers can include fibers derived from the fruit of a plant, such as coconut fibers. Vegetable-derived fibers can include fibers derived from the stalk of a plant, such as wheat, rice, barley, bamboo, and grass. Vegetable-derived fibers can include wood fibers.

Animal-derived fibers typically comprise proteins, e.g., wool, silk, mohair, and the like. Animal-derived fibers can be derived from animal hair, e.g., sheep's wool, goat hair, alpaca hair, horse hair, etc. Animal-derived fibers can be derived from animal body parts, e.g., catgut, sinew, etc. Animal-derived fibers can be collected from the dried saliva or other excretions of insects or their cocoons, e.g., silk obtained from silk worm cocoons. Animal-derived fibers can be derived from feathers of birds.

Mineral-derived natural fibers are obtained from minerals. Mineral-derived fibers can be derived from asbestos. Mineral-derived fibers can be a glass or ceramic fiber, e.g., glass wool fibers, quartz fibers, aluminum oxide, silicon carbide, boron carbide, and the like.

Disclosed herein are methods for combining two or more different populations of fibers so that they can together form a composite material. In embodiments, the composite material can be formed as a fibrous web. It is understood by those having ordinary skill in the art that differences in surface energies between certain fiber populations (e.g., hydrophobic synthetic fibers and hydrophilic cellulose fibers) can prevent their being combined into composite materials. Disclosed herein are methods for modifying the surface chemistry of such dissimilar fiber populations to enable them to be attached to each other to form composite materials such as fibrous webs having desirable properties.

In embodiments, a population of fibers of one type can first be dispersed in an appropriate medium and then functionalized with a polycation such as a polyamine. As used herein, the term “polycation” may include any polymer (e.g., copolymer) having a net positive charge. As used herein, the term “polyamine” may include any polymer or copolymer that has at least a portion of its repeat units containing an amine (quaternary, ternary, secondary, or primary). In embodiments, the polyamine may desirably contain some repeat units with primary amines due to the reactivity of a primary amine.

The polymers (e.g., polycations) as used herein can have an average molecular weight which can range from 1,000 up to 10,000,000 but it is preferable to be between 10,000 to 500,000. In other embodiments, however, polymers can include oligomers, e.g., having 5 or 10 to about 20 repeat units found in the corresponding polymer. In embodiments, a polyamine may be a polymer comprising chitosan or polyethyleneimine. In embodiments, a chitosan polymer may comprise a certain portion of higher molecular weight chitosan, i.e., chitosan with a viscosity of at least 800 cp when in a 1% acetic acid solution. In embodiments, the amount of higher molecular weight chitosan may be greater than 10%, greater than 20%, or greater than 30%. Those of skill in the art will appreciate that for certain polymers, e.g., chitosan, an exact molecular weight may not be available, because such structures are defined by viscosity rather than molecular weight.

A process for manufacturing a composite material for fibrous webs may involve initially dispersing a population comprising a selected microfiber, larger fiber, or combination thereof, in an aqueous or solvent medium such as isopropanol/water mixtures to form a dispersion or slurry, and then functionalizing the fibers of the population with a polycation (e.g., polyamine), or utilizing some other binder component such as a wet strength component. The selected polycation may be added directly to the fiber or microfiber dispersion or slurry. As used herein, the term “addition level” refers to the weight of a polycation compared to the weight of the selected fiber or microfiber. In embodiments, an addition level of 0.1% to 5.0% (based on weight of the microfiber) is desirable, or an addition level of 0.5% to 2%.

Once a suitable concentration of fiber or microfiber polycation solution has been achieved, the polycation may be linked to the fiber or microfiber using a coupling agent, for example crosslinkers with isocyanates, epoxides, or anhydrides. Such coupling agents are advantageous, for example, when working with synthetic fibers or microfibers. Any multifunctional crosslinking agent can be used that reacts with the polycation and the fiber or microfiber if a covalent bond is desired. Alternatively, the polycation may be attached to the fiber or microfiber substrate through electrostatic, hydrogen bonding, or hydrophobic interactions. The polycation can spontaneously self-assemble onto the fiber or microfiber surface, for example, or it can be precipitated onto the surface.

Chitosan, for example, may be precipitated onto a fiber or microfiber surface. Because chitosan is only soluble in an acidic solution, it may be precipitated onto the fibers or microfibers in a solution by adding base to a polyamine-fiber/microfiber dispersion until the chitosan precipitates onto the fibers or microfibers.

In embodiments, following functionalization with the polycation, one or more complementary polymers may be added to the process. A complementary polymer can to be any polymer that either interacts with the polycation (e.g., reacts to the amines on a polyamine). In the case where the complementary polymer does not react, the interaction can either be electrostatic, hydrogen bonding, or other secondary interaction. Advantageously, an electrostatic interaction will be achieved, using, for example a polyanion such as one containing carboxylic acid groups. Examples of suitable polyanions include biopolymers such as pectin, xanthan gum, and carboxymethyl cellulose and synthetic polymers such as polyacrylic acid or polymethacrylic acid. Copolymers can also be used, for example those that contain repeat units with anionic charge.

In the case where the complementary polymer reacts with the functionalities on the polycation (e.g., amines on a polyamine), the complementary polymer can contain repeat units with any group that reacts with polycation functionality. In the case of amines on a polyamine, such groups include but are not limited to epoxides, anhydrides, carboxylic acids, and isocyanates. In embodiments, copolymers may be used that contain some repeat units with reactive groups, for example reactive groups like those mentioned above. The molecular weight of the polymer may advantageously be between 1,000 and 10,000,000 Daltons, for example between 10,000 and 500,000.

As would be understood by skilled artisans, secondary polymers can also be added that interact with the complementary polymers. Such secondary polymers can impart specific functionality to the composite, or they can stabilize it or improve its properties in other ways. For example, secondary polymers can include copolymers containing ionic groups, or containing hydrophobic groups such as styrene maleic anhydride or styrene maleimides, or the like, which can be specifically precipitated onto fibers using changes in pH, thereby providing a water-resistant layer on the fiber surfaces. Secondary polymers also can be added after the fiber assembly is in place, so that they form a passivation layer and change the surface properties of the resulting sheet. In embodiments, secondary complementary polymers can include proteins such as zein (from corn), which can be precipitated onto the composite by pH change. Such proteins are hydrophobic in nature and are grease-resistant, lending these desirable properties to a composite material.

In embodiments, the complementary polymer may enhance the strength of the composite. In other embodiments, the complementary polymer may contain functionality that can impart properties besides strength enhancement. For example, elastic polymers or copolymers can be used to change the resulting product's stiffness or wear resistance, or hydrophobic polymers or copolymers can be used to change the water contact angle. Combinations of suitable polymers can also be used. The addition level is preferred to be from 0.1% to 5.0% (based on microfiber weight) and further preferred between 0.5% and 2%.

After a first population of fibers or microfibers has been functionalized, and after a complementary polymer has been added, a second population of non-functionalized fibers or microfibers can be added to the mixture. A wet-strength agent can then be added to the mixture to bind the two populations of fibers together for the formation of a fibrous sheet or web. The second population of non-functionalized fiber can include any fiber or microfiber. Not to be bound by theory, it is understood that the functionalization of the first fiber population before its addition to the second population of fibers can minimize the electrostatic repulsion that might otherwise exist between the two fiber populations. These methods can thus permit the admixture of dissimilar types of fibers for the formation of a fibrous web or sheet.

In some embodiments, after addition of any complementary polymer, a treated microfiber may be mixed with larger fibers to form a mixture, for example a slurry. Mixing techniques may involve any technique familiar to skilled artisans, for example mixing in solution or mechanical mixing. In embodiments, the larger fibers may comprise any fibrous material. As an example, larger fibers may comprise cellulosic fibers, e.g., wood pulp. From this microfiber-larger fiber mixture, a fibrous web may be produced, for example as a sheet, using techniques familiar to skilled artisans. As an example, synthetic fibers or microfibers treated with chitosan could be combined with cellulose wood pulp with a wet strength agent to produce cleaning towels with an increased surface area and oleophobicity that helps in cleaning oily spills. The ratio of microfiber to larger fiber as a percentage by weight can range widely to achieve specifications for a particular product. In embodiments, the ratio of microfiber to larger fiber may approach 0%, or it may approach 100%. Appropriate ratios for specific articles of manufacture may be determined by skilled artisans using no more than routine experimentation. In alternative embodiments, the larger fiber can be treated by any of the techniques discussed herein before being mixed with microfibers, which may or may not be treated.

In embodiments, a mixture whose fibrous component contains between 10% to 60% microfiber by weight may provide advantages for performance and/or cost-effectiveness. For example, the microfibers can help maintain product integrity during both wet and dry cleaning, or may reduce particulate shedding. Use of hydrophilic microfibers may enhance absorptive or fluid retention. Microfibers may increase the strength of the sheet during wet or dry uses. Other performance advantages may be readily appreciated by those of ordinary skill in the art, and these advantages may be readily attained using no more than routine experimentation.

In embodiments, a wet strength chemical may be added to the mixture at a level of 0.05% to 5.0% (based on weight of all fiber) but preferably from 0.2% to 2%. Wet strength chemicals include commercially available agents used in papermaking to aid in immobilization of bonds between fibers in a wet state by covalent bond formation. Examples of wet strength chemicals include melamine-formaldehyde resins, urea-formaldehyde resins, and epoxidized polyamine-polyamide resins, and other such chemicals known to those skilled in the art. To enhance wet strength or other properties, any prepolymer or polymer can be added that covalently binds the treated microfibers to the other fibers. Examples of specific wet strength chemicals include the chemical series with the trade name, Kymene (made by Hercules).

In order to functionalize microfibers according to these methods to combine them with larger fibers, any process that disperses the microfibers appropriately can be used to apply the polymers to the microfibers. Processes include various mixing processes such as pulping, shear mixing, stirring. In addition to mechanically mixing, any other known dispersion process can be used such as blowing a gas into the fibers. The treated microfibers can be mixed in with the fibers using any known process. In embodiments, any known mixing process may be used for any of the steps. In other embodiments, specific mixing processes may be devised and adapted for the technology by skilled artisans, using no more than routine experimentation. In embodiments, the treated microfibers may be produced first, then combined with larger fibers to make the fibrous product. In embodiments, the treated fibers may be added to a fibrous product that has already been partially formed. Variations will be readily apparent to those of ordinary skill in the art.

Some particular embodiments are drawn to methods for forming fiber compositions or composite materials by treating at least two populations of fibers or microfibers in different manners. In some embodiments, one population of fibers is treated with a polycation component, such as any type of, or combination of, polyamine as described within the present application (e.g., chitosan and/or a polyalkyleneimine having 2 to 10 carbon atoms in the backbone per repeat unit). Another population of fibers can exhibit a net negative charge. For instance, the net negative charge can be inherent to the fiber population (e.g., cellulosic fibers), or the fibers can be treated in a manner such that a net negative charge is imparted (e.g., having polyanions attached to the fibers such as any combination of types of complementary polymers discussed in the present application). These two populations can be combined in a mixture, which can subsequently be used to form a fiber composition, such as forming a sheet of a paper-based material. While not necessarily being bound by any particular theory, such embodiments can result in a fiber composition that has enhanced strength, and/or abrasion resistance, relative to subjecting both populations to exactly the same conditions because of the electrostatic attraction between the different net charged fibers.

In various embodiments, the population of fibers that are treated with a polycation can be a population of microfibers or a population of larger fibers. For example, microfibers can be treated with a polycation (e.g. one or more polyamines) while larger fibers can exhibit the net negative charge. Also, the types of fibers used in various fiber populations can be of any type, such as those disclosed in the present application (e.g., naturally-occurring fibers such as cellulosic fibers, and/or synthetic fibers such as polypropylene fibers, and/or fibers that comprise a plurality of fibrils that are held together or separated). For example, one fiber population may comprise Nomex fibers for improved fire retardancy, metallic fibers for improved conductivity, ferrous fibers for magnetic properties.

In an embodiment, two populations of fibers that are substantially similar in size and base chemical nature (e.g., cellulosic fibers having the same average diameter and length) can be used with one being treated with a polycation (e.g., polyamine) and the other being untreated. As well, more than two populations of fibers can be treated in various manners. It is apparent that these embodiments can utilize any of the other features described in other embodiments of the present invention (e.g., the use of wet strength components, complementary polymers, coupling agents, etc.).

Though several embodiments described herein refer to treating and treated microfibers, aspects of the present application also include utilizing any combination of the treatments described herein on the larger fiber component. In some embodiments, treatment of larger fibers can be accomplished with synthetic long fibers. Exemplary treatments include the addition of polycations (e.g., polyamines), coupling agents, complementary polymers, secondary polymers, and wet strength agents, among others. In other embodiments, each population can be subjected to a different type of treatment (e.g., one population treated with polyamine, the other population being treated with a complementary polymer).

The methods for treating fiber populations disclosed herein can enable the manufacture of products having distinct and advantageous properties. For example, synthetic microfibers can be mixed with cellulosic woodpulp longer fibers after carrying out the treatments disclosed herein, and their mixture can be used to create filtration membranes. In such a product, the surface area and the porosity of the filtration membrane would be determined by the selection of an appropriate microfiber, and/or the determination of the ratio of microfibers to longer fibers. By selecting fibrillated nano- and microfibers, for example, a filtration membrane can be produced with a specific porosity and surface chemistry. In embodiments, the porosity can be controlled by adding a preselected amount of nano- or microfibers to the manufacturing process, with treatments as disclosed herein. In embodiments, the surface chemistry of the cellulosic and synthetic fibers can be changed by attaching selected polymers to the fiber surface to make them more hydrophilic or hydrophobic (e.g., chitosan analogs). For filtration membranes and other applications where low protein binding is necessary (such as biological applications and medical applications), synthetic and natural fibers can have further surface modifications, using, for example, polymers that contain PEG-like moieties (Jeffamines, Pluronics, Tectonics, chitosan analogs, and the like).

In another embodiment, the synthetic fibers can be coated with a polysaccharide layer, so that the synthetic fibers possess surface characteristic of regular wood pulp. Fibers modified in this way can mimic the surface properties of natural pulp fibers, while possessing the mechanical and thermal properties of synthetic materials from which they are made. Exemplary fibers can have a long axis and a small diameter, so that their aspect ratio is large. An aggregation of such fibers, having a large aspect ratio, can form what is termed a percolation network even though present in very dilute, low loading levels in the final mixture. As a result of the scaffolding effect of the percolation network, a paper made using such fibers can be very strong. A paper made using such fibers can also be light in weight if lower density fibers are used, e.g., polyolefins and the like.

Cellulosic molecules and polysaccharides such as carboxymethylcellulose, dextran, various gums such as xanthan gum, gum Arabic can be used to modify the surfaces of synthetic fibers. As the synthetic fibers often lack the functionalities for easy chemical modification and attachment, an intermediate layer can be provided such that it attaches the polysaccharide or cellulosic molecules to the surface of the synthetic fibers. As an example, the desired synthetic fibers can be initially coated with a layer of polycations such as chitosan or similar polyamines or substituted polyamines and then exposed to anionic polysaccharide derivatives. The surface of the synthetic fibers can be electrostatically modified using this method so that it possesses advantageous properties of cellulose fibers, such as are found in regular wood pulp. Fibers modified using this method can also be further stabilized by crosslinking the cellulosic molecule to the surface of synthetic fibers by using traditional crosslinkers such as glyoxal, glutaraldehyde.

Such mixtures of coated synthetic fibers and natural pulp fibers can furthermore be assembled together using certain of the methods set forth herein. In other embodiments, a synthetic fiber such as polyester can be spun and cut to produce short fiber strands that mimic the dimensions of the cellulosic fibers used, for example, in paper manufacture. The synthetic fibers can then be coated with a layer of cellulose or cellulosic materials, such as dextran, starch, alkoxy-substituted cellulose, carboxymethy-cellulose, or other derivatized cellulosic materials.

In embodiments, the overcoat layer can be internally crosslinked and/or anchored on polyester with well known crosslinkers such as polyacrylic acid, DMDHEU, and BTCA, etc. Crosslinking can attach the overcoat to the fiber securely, so that it is not dislodged during slurry formation and papermaking. The resulting synthetic-based modified fibers can mimic natural fibers in dimension and in surface characteristics. They can thus be evenly distributed throughout a paper product, so that a paper product formed from them can resemble one made from natural fibers. In a state of full dispersion, where most of the modified fibers exist in isolation except for point contacts with other co-existing components, the aspect ratio (length vs. diameter) of such fillers can be large, so even a small volume fraction loading of the modified synthetic fibers can create a continuous network over a macroscopic sample. The continuous reinforcement network leads to enhanced mechanical performance. In embodiments where such coated fibers are more or less randomly oriented in the x,y plane (thus exhibiting an even in-plane angular distribution), the resulting products can also demonstrate greatly enhanced puncture resistance and tear resistance.

In yet other embodiments, a modified synthetic fiber can be created having a hydrophilic surface that is charged or that possesses a high level of hydration when mixed into the slurry. For example, a polymeric fiber such as a polyester or a polyamide (e.g., nylon) having a neutral charge can be given a highly hydrophilic surface treatment by anchoring a molecular network made of a hydrophilic polymer (such as polyacrylic acid) on the fiber surface. Other examples will be appreciated by artisans having ordinary skill in the art. Such modified fibers can be dispersed evenly throughout a system, because they do not tend to aggregate. Moreover, since the modified fibers do not bunch up, the high aspect ratio intrinsic to individual fibers is preserved, allowing the fibers to be used as effective reinforcement agents. In embodiments, surface modifications are performed as a separate, “off-line” step, with the modified fibers being introduced into the paper-making slurry only thereafter.

Other embodiments are drawn to chitosan analogues that can be prepared with synthetic polyamines, which can be used with any appropriate embodiment herein. Chitosan analogues refer to polymers (e.g., polycations) that, like chitosan, can be in solution at a pH below a given threshold and can precipitate out of solution when the pH is raised above the threshold. The pH threshold can be selected to be any value, e.g., a value above a pH of about 2, 3, 4, 5, or 6, and/or a pH below about 6, 7, 8, 9, or 10. One instance of a chitosan analogue refers to hydrophobically modified polycations (e.g., polyamines) that can be utilized with embodiments herein, i.e., modifying a non-chitosan polycation (e.g., polyamine excluding chitosan) with a hydrophobic group in a manner to act as a chitosan analogue. The degree of substitution can control the pH transition point. For example, polyvinylamine (Lupamin 9095, BASF) can be modified with hydrophobic side groups by the use of monoepoxy functionalized alkyl chains of varying length by dissolving various amounts of the epoxy functionalized compound with polyvinylamine in a common solvent such as acetone. The stoichiometry of substitution of the alkyl chain onto the polyvinylamine backbone can be controlled by the amount of the epoxy functionalized alkyl chain in the reaction mixture.

In another example, polyvinylamine (Lupamin 9095, BASF) can be modified using epoxy functionalized polyethyleneoxide (PEO) and polypropyleneoxide (PPO) polymers by dissolving the polymers in a common solvent such as acetone. The PEO and PPO polymers exhibit lower critical solution temperatures (LCST), which can be exploited to alter the solution behavior of modified polyvinylamines. By varying the ratio of PEO to PPO attached to the polyamine backbone, the transition temperature at which the modified polyamine precipitates in the aqueous solution can be controlled. The choice of polyamine would not be not limited to polyvinylamine but is inclusive of polyamines such as polyethyleneamine (branched or linear) and polyallylamine.

Still other embodiments can be directed to polyamines modified with PEO and/or PPO segments. For example, a modified polyvinylamine, prepared according any of the methods described herein, can be dissolved in water and the temperature of the solution was initially cooled to about 5° C. and then slowly raised to 90° C. and the temperature at which the solution turns cloudy or turns clear from cloudy is noted.

Some embodiments of the present invention are direct to handsheets having fire-retardant properties. For instance, Nomex® meta-aramid fibers of 2 mm length at 2 denier can be mixed with cellulose woodpulp, e.g., prepared according to the protocol described in Examples 2 and 9 below. Nomex® is understood to have fire-resistant properties when incorporated into fabrics or sheets. A handsheet prepared according to the aforesaid method using Nomex® fibers would be expected to demonstrate fire-resistant properties.

Other embodiments are directed to compositions that impart protein adsorption to resistance to a fibrous composition. For instance, samples, e.g., prepared in accord with the techniques described in Example 9 below, can be treated with 1% solution of polyetheramine such as Jeffamine XTJ502 (Huntsman Chemicals) by dipping the handsheet in the solution for 10 min. The handsheet can be removed from the beaker, rolled between 2 couch sheets to remove excess water and dried. Alternately, polyethyleneglycol-containing polymers with anhydride or epoxy function groups could be used to prepare handsheets. Specifically, handsheets, e.g., prepared in Example 9 below, can be dipped in polyethyleneglycol diglycidylether at 1% in water for 10 min. The handsheets can be removed from the solution, rolled between 2 couch sheets to remove excess water and dried. The amine-functionalized handsheets prepared according to these methods would be expected resist protein adsorption, because the polymers incorporated into the paper can prevent the binding of proteins to the underlying cellulose surfaces.

Some embodiments are directed to preparing handsheets having conductive properties. For instance, handsheets can be prepared, e.g., according to the protocol in Examples 2 and 9 below, using metallic fibers. In a particular example, fibers such as metallized polyester yarn (Melton Corp) and Lurex brand aluminized polyester and Nylon yarns from Lurex Co. Ltd can be used. Because of the conductive properties of the metallic fibers, a handsheet prepared according to the aforesaid examples would be expected to have conductive and anti-static properties.

Other embodiments are direct to preparing filter papers. Advanced filter papers can be made using the formulations and methods described in the present application. Filter papers, which are cellulosic in nature, could be strengthened using polysaccharide-coated synthetic fibers such that the chemical nature of fibers is unaffected while improving the burst strength of the filter paper. For instance, filter papers could be made using procedure as described in Examples 2 and 9 below using different microfibers to impart different functionalities to the filter paper. Use of synthetic microfibers such as polyolefin fibers or Nylon/polyester bicomponent fibers imparts hydrophobicity to the filter paper which can be used to trap hydrophobic moieties present in water including proteins, allowing more expensive 100% synthetic filters to be replaced with inexpensive synthetic/cellulose composite filters. Further, the amine functionalized synthetic fibers can be functionalized with specific molecules such as metal-chelating agents, antibodies, and the like, to produce “intelligent” filtration membranes to selectively remove desired contaminants. In addition to the above advantages, synthetic microfibers can also provide higher surface area and an ability to control the pore size of the filtration membrane that is not possible by coarser cellulose fibers. In addition, the procedure outlined earlier could be used to impart protein resistance to filtration membranes to prevent clogging of pores by protein based films leading to loss of filtration efficiency.

Yet other embodiments are directed to the use of nanofibrillated cellulose to produce stronger paper. The strength of papers made with cellulose can be limited because the contact points between the cellulose fibers due to hydrogen bonding are limited in number. Paper strength can be improved by the use of smaller cellulose fibers made using fibrillation. Nanofibrillated wood pulp fibers (Engineered Fibers Technology, LLC) could be used to increase effective surface area of fibers and to increase hydrogen bonding density between fibers by increasing the number of contacts between more flexible nano fibers and coarser cellulose wood pulp fibers. Composite products made in this way could be further strengthened by the procedures detailed in Examples 2 and 9 below.

EXAMPLES

The examples that follow illustrate some of the systems and methods disclosed herein by describing certain embodiments and features of fibrous webs and sheets manufactured in accordance with these systems and methods. The Examples are in no way intended to limit the scope of the present invention. In the Examples provided, certain of the following materials were used, as described in more detail below.

Materials Acrylic Microfiber

Engineered Fibers Technology, A010-4

Shelton, Conn.

Chitsan cg800

Primex

Siglufjodur, Iceland

Chitosan cg110

Primex

Siglufjodur, Iceland

Kymene 557H

Hercules 96-23-1

Wilmington, Del.

Lyocell Microfiber

Engineered Fibers Technology, L010-4, L040-6

Shelton, Conn.

Nylon/PET Microfiber

Poly(acrylamide-co-acrylic acid), Partial Sodium Salt

Aldrich 411471-250G

Milwaukee, Wis.

Poly(ethylene glycol) diglycidyl ether

Aldrich 475696

St. Louis, Mo.

Poly[(isobutylene-alt-maleic acid), ammonium salt-co-(isobutylene-alt-maleic anhydride)]

Aldrich 531367-250G

St. Louis, Mo.

Polypropylene Microfiber

HILLS, Inc.

W. Melbourne, Fla.

Larger Fiber

Softwood Pulp Cellulose Fibers

Blotting sheets

Kalamazoo Paper Chemicals

Richland, Mich.

Example 1 Larger Fiber Pulp Preparation

A 5% slurry was prepared by blending 20 g refurnished long fibers in 400 mL of water. The slurry was diluted to 0.5% pulp by adding 3.6 L of water.

Example 2 Microfiber Pulp Preparation

A 5% slurry was prepared by blending 20 g lyocell microfibers (L010-4, L040-6, acrylic, polypropylene, or nylon/PET) in 400 mL of water. The slurry was diluted to 0.5% pulp by adding 3.6 L of water.

Example 3 Handsheet Preparation

Handsheets were prepared using a Mark V Dynamic Paper Chemistry Jar and Hand-Sheet Mold from Paper Chemistry Laboratory, Inc. (Larchmont, NY). The appropriate volume of 0.5% pulp slurry (50/50 slurry, long fiber slurry or microfiber slurry) was functionalized with up to 2% the of the appropriate polymer(s) (based on dry weight). Polymer additions were done at 10 minute intervals. This combined slurry was diluted with water up to 2 L and added to the handsheet maker. The slurry was mixed at a rate of 1100 RPM for 5 seconds, 700 RPM for 5 seconds, and 400 RPM for 5 seconds. The water was then drained off. The subsequent sheet was then transferred off of the wire, pressed and dried.

Example 4 Abrasion Testing

Abrasion tests were performed on the handsheets by wetting the sheet and using a 2 kg weight to rub the sheet across black felt ten times. The amount of lint left on the felt by the sheet was turned into a percentage where 0% was no lint and 100% was the weight tearing through the sheet leaving lint that covered most of the rubbed area.

Example 5 Mixed Fiber Pulp Slurry Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of the material from Example 1 combined with 150 mL of material from Example 2 (L010-4). The abrasion test could not be performed because of inadequate wet strength.

The wet tensile strength was 0.885 lbf/in at the max load/width. The wet to dry strength was 10.8%.

Example 6 Mixed Fiber Pulp Slurry with Chitosan Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of the material from Example 1 combined with 150 mL from Example 2 (L010-4) and adding 1.5 mL of a 1% CG800 chitosan solution. The abrasion test could not be performed because of inadequate wet strength. The wet tensile strength was 2.098 lbf/in at the max load/width. The wet to dry strength was 17.2%.

Example 7 Mixed Fiber Pulp Slurry with Kymene Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of the material from Example 1 combined with 150 mL from Example 2 (L010-4). To this 0.12 mL of 12.5% Kymene 557 solution was added. The abrasion test left 30% of the felt covered. The wet tensile strength was 5.456 lbf/in at the max load/width. The wet to dry strength was 47.1%.

Example 8 Microfiber with Chitosan and Kymene Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of the material from Example 2 (L010-4) and adding 0.75 mL of a 1% CG800 chitosan solution. The slurry was then combined with 150 ml of the material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added. The abrasion test left 5% of the felt covered in lint. The wet tensile strength was 6.836 lbf/in at the max load/width. The wet to dry strength was 54.4%.

Example 9 Microfiber with Chitosan, Polyacrylamide and Kymene Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of the material from Example 2 (L010-4) and adding 0.75 mL of a 1% CG800 chitosan solution then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of the material produced in Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added. The abrasion test left 1% of felt covered in lint. The wet tensile strength was 5.769 lbf/in at the max load/width. The wet to dry strength was 52.6%.

Example 10 Long Fiber with Chitosan, Polyacrylamide and Kymene Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of the material from Example 1 and adding 0.75 mL of a 1% CG800 chitosan solution then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of the material produced in Example 2 (L010-4). To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 11 6 mm Microfiber with Kymene Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of the material from Example 1 combined with 150 mL of material from Example 2 (L040-6). To this 0.12 mL of 12.5% Kymene 557 solution was added. The abrasion test left 20% of the felt covered. The wet tensile strength was 4.426 lbf/in at max load/width. The wet to dry strength was 36.7%.

Example 12 6 mm Microfiber with Chitosan, Poly(acrylamide-co-acrylic acid) and Kymene Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of the material from Example 2 (L040-6) and adding 0.75 mL of a 1% CG800 chitosan solution then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of the material produced in Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added. The abrasion test left 20% of the felt covered. The wet tensile strength was 4.426 lbf/in at max load/width. The wet to dry strength was 36.7%.

Example 13 Acrylic Microfiber with Kymene Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 1 combined with 150 mL of material from Example 2 (acrylic). To this 0.12 mL of a 12.5% Kymene solution was added. The abrasion test left 1% of the felt covered in lint. The wet tensile strength was 6.574 lbf/in at the max load/width. The wet to dry strength was 67.3%.

Example 14 Acrylic Microfiber with Chitosan, Poly(acrylamide-co-acrylic acid) and Kymene Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (acrylic) and adding 0.75 mL of a 1% CG800 chitosan solution then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of material produced in Example 1. To this 0.12 mL of a 12.5% Kymene solution was added. The abrasion test left 1% of the felt covered in lint. The wet tensile strength was 4.911 lbf/in at the max load/width. The wet to dry strength was 67.9%.

Example 15 Polypropylene Microfiber with Kymene Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 1 combined with 150 mL of material from Example 2 (polypropylene). To this 0.12 mL of a 12.5% Kymene solution was added. The abrasion test could not be performed because of inadequate wet strength. The wet tensile strength was 0.434 lbf/in at the max load/width. The wet to dry strength was 35.6%.

Example 16 Polypropylene Microfiber with Chitosan, Poly(acrylamide-co-acrylic acid) and Kymene Handsheet Tests

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (polypropylene) and adding 0.75 mL of a 1% CG800 chitosan solution then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of material produced in Example 1. To this 0.12 mL of a 12.5% Kymene solution was added. The abrasion test left 10% of the felt covered in lint. The wet tensile strength was 1.4 lbf/in at the max load/width. The wet to dry strength was 85.3%.

Example 17 Mixed Fiber Pulp Slurry with Chitosan and Polyanhydride

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 1 combined with 150 mL of material from Example 2 (L010-4) and adding 1.5 mL of a 1% CG800 chitosan solution. To this 1.5 mL of a 1% maleic anhydride copolymer solution was added.

Example 18 Mixed Fiber Pulp Slurry with Chitosan and Epoxide

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 1 combined with 150 mL of material from Example 2 (L010-4) and adding 1.5 mL of a 1% CG800 chitosan solution. To this 1.5 mL of a 1% polyethylene glycol diglycidyl ether solution was added.

Example 19 Mixed Fiber Pulp Slurry with Chitosan and Polyanhydride

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 1 combined with 150 mL of material from Example 2 (L010-4) and adding 1.5 mL of a 1% CG800 chitosan solution. After the sheet was formed, it was dipped into a 1% solution of a maleic anhydride copolymer.

Example 20 Mixed Fiber Pulp Surry with Chitosan and Jeffamine Substituted Polyanhydride

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 1 combined with 150 mL of material from Example 2 (L010-4) and adding 1.5 mL of a 1% CG800 chitosan solution. To this 1.5 mL of a maleic anhydride copolymer was added with 25% of the anhydrides substituted with jeffamine.

Example 21 Mixed Fiber Pulp Slurry with High pH

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 1 combined with 150 mL of material from Example 2 (L010-4) and adding 1.5 mL of a 1% CG800 chitosan solution. To this 0.1 M NaOH was added until the pH reached 8 and then 1,5 mL of 1% maleic anhydride solution was added.

Example 22 Microfiber with Half Chitosan, Poly(acrylamide-co-acrylic acid) and Kymene

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (L010-4) and adding 0.375 mL of a 1% CG800 chitosan solution and then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 23 Microfiber with Chitosan, Half Poly(acrylamide-co-acrylic acid) and Kymene

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (L010-4) and adding 0.75 mL of a 1% CG800 chitosan solution and then 0.375 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 24 Microfiber with Chitosan, Polyacrylic Acid and Kymene

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (L010-4) and adding 0.75 mL of a 1% CG800 chitosan solution and then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylic acid) solution. The slurry was then combined with 150 mL of material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 25 Microfiber with Short Chitosan, Polyacrylamide and Kymene

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (L010-4) and adding 0.375 mL of a 2% CG110 chitosan solution and then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 26 Microfiber with Chitosan, Larger Fibers with Poly(acrylamide-co-acrylic acid), Kymene

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (L010-4) and adding 0.75 mL of a 1% CG800 chitosan solution. Separately, 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) was added to 150 mL of the material produced in Example 1. The two slurries were then combined. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 27 Microfiber with Chitosan, Polymaleic Anhydride and Kymene

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (L010-4) and adding 0.75 mL of a 1% CG800 chitosan solution and then 0.75 mL of a 1% maleic anhydride copolymer solution. The slurry was then combined with 150 mL of material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 28 4% Microfiber Slurry

Two handsheets were produced according to the method of Example 3 using 15 g of a 5% microfiber slurry (L010-4) that was diluted with 3.75 mL of water. To this slurry 0.75 mL of a 1% CG800 chitosan solution and then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 29 1% Microfiber Slurry

Two handsheets were produced according to the method of Example 3 using 15 g of a 5% microfiber slurry (L010-4) that was diluted with 60.25 mL of water. To this slurry 0.75 mL of a 1% CG800 chitosan solution and then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 30 3% Microfiber Slurry

Two handsheets were produced according to the method of Example 3 using 15 g of a 5% microfiber slurry (L010-4) that was diluted with 10.75 mL of water. To this slurry 0.75 mL of a 1% CG800 chitosan solution and then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 31 50% Mixture of Low and High Molecular Weight Chitosan

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (L010-4) and adding 0.75 mL of a chitosan solution. The chitosan solution was premixed to make a 50% CG800 and 50% CG110 solution. To this 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution was added. The slurry was then combined with 150 mL of material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 32 Microfiber with Chitosan, Polyanhydride and Kymene

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (L010-4) and adding 0.75 mL of a 2% CG110 chitosan solution and then 0.75 mL of a 1% poly[(isobutylene-alt-maleic acid), ammonium salt-co-(isobutylene-alt-maleic anhydride)]. The slurry was then combined with 150 mL of material from Example 1. To this 0.12 mL of 12.5% Kymene 557 solution was added.

Example 33 Nylon/PET Microfiber with Kymene

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 1 combined with 150 mL of material from Example 2 (nylon/PET). To this 0.12 mL of a 12.5% Kymene solution was added.

Example 34 Nylon/PET Microfiber with Chitosan, Poly(acrylamide-co-acrylic acid) and Kymene

Two handsheets were produced according to the method of Example 3 using 150 mL of material from Example 2 (nylon/PET) and adding 0.75 mL of a 1% CG800 chitosan solution then 0.75 mL of a 1% poly(acrylamide-co-acrylic acid) (80% acrylamide) solution. The slurry was then combined with 150 mL of material produced in Example 1. To this 0.12 mL of a 12.5% Kymene solution was added.

Equivalents

While specific embodiments of the subject invention have been discussed, the above specification is illustrative and not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of this specification. For instance, embodiments of the present invention can utilize any combination of features from other embodiments combined in any feasible permutation to provide other aspects of the present invention. In one example, microfibers and/or larger fibers can be treated with any one or more of the components described herein, such as polycations, complementary polymer, secondary polymer, wet strength chemical, etc. In a particular example, microfibers and larger fibers can be treated by Kymene and no other components. The full scope of the invention should be determined by reference to the claims, along with their full scope of equivalents, and the specification, along with such variations.

Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. 

1. A fibrous composition of mixed fibers, comprising: a first population of fibers; a second population of fibers having native surface characteristics differing from native surface characteristics of the first population of fibers, at least one population of fibers being surface modified by a polycation, the first and second population of fibers being mixed together in the form of a porous composition.
 2. The composition of claim 1, wherein the fibrous composition comprises a sheet structure.
 3. The composition of any preceding claim 1, wherein the polycation comprises a polyamine.
 4. The composition of claim 1, wherein at least one surface modified population of fibers comprises synthetic fibers.
 5. The composition of claim 1, wherein at least one surface modified population of fibers comprises fibers exhibiting a native hydrophobic surface.
 6. The composition of claim 5, wherein the native hydrophobic surface is surface modified to a hydrophilic surface.
 7. The composition of claim 1, wherein at least one population of fibers comprises natural fibers.
 8. The composition of claim 1, wherein at least one population of fibers comprises at least one of microfibers and larger fibers.
 9. The composition of claim 1, wherein at least one population of fibers comprises fibers having dissimilar sizes.
 10. The composition of claim 1, wherein the polycation is bound to at least one fiber using a coupling agent.
 11. The composition of claim 1, wherein at least one population of surface modified fibers is attached to the polycation by at least one of electrostatic interactions, covalent bonding, hydrogen bonding, and hydrophobic interactions.
 12. The composition of claim 1, wherein the polycation couples at least two fibers together.
 13. The composition of claim 1, further comprising: a complementary polymer capable of attractively interacting with the polycation.
 14. The composition of claim 13, wherein the complementary polymer comprises at least one of a pectin, xanthan gum, carboxymethyl cellulose, polyacrylic acid, polymethacrylic acid, polyacrylamide, polyethylene glycol, polymers derived from maleic anhydride, and copolymer having at least one segment comprising any of the aforementioned polymers.
 15. The composition of claim 13, wherein the complementary polymer comprises at least one of an epoxide, an anhydride, a carboxylic acid, and an isocyanate.
 16. The composition of claim 1, further comprising a wet strength component.
 17. The composition of claim 16, wherein the wet-strength component comprises at least one of a melamine-formaldehyde resin, a urea-formaldehyde resin, and an epoxidized polyamine-polyamide resin.
 18. The composition of claim 1, wherein the polycations comprises polycations modified with hydrophobic side groups.
 19. The composition of claim 1, wherein at least one surface modified population of fibers comprises a polysaccharide coupled to at least one of the fibers.
 20. The composition of claim 1, wherein at least one surface modified population of fibers comprises synthetic fibers having a cellulose-based material coupled thereto.
 21. The composition of claim 19, further comprising: a crosslinker for coupling the surface modification to at least one of a fiber and another portion of the surface modification.
 22. The composition of claim 1, wherein at least one population of fibers comprises at least one of a fire-retardant material, an electrically conductive material, a nanofibrillated cellulose-based material.
 23. The composition of claim 1, wherein at least one surface modified population of fibers exhibits protein adsorption resistance relative to a native surface of the surface modified population of fibers.
 24. The composition of claim 1, wherein the composition is at least a portion of a filter paper.
 25. A method for forming a mixed fiber composition, comprising: attaching polycations to a first population of fibers; providing a second population of fibers having native surface characteristics differing from native surface characteristics of the first population of fibers; forming a precursor fiber composition comprising the first population of fibers and the second population of fibers; and creating a sheet structure from the precursor fiber composition.
 26. The method of claim 25, wherein the step of attaching polycations comprises precipitating the polycations onto the first population of fibers.
 27. The method of claim 26, further comprising: attaching a coupling agent to the polycations.
 28. The method of claim 25, further comprising: adding a wet strength component to the fiber composition.
 29. The method of claim 28, wherein the step of adding the wet strength component comprises adding the wet strength component after mixing the first population of fibers and the second population of fibers together.
 30. The method of claim 25, further comprising: adding a complementary polymer having an anionic portion to the first population of fibers; and attaching the complementary polymer to the at least one of the polycations.
 31. The method of claim 25, wherein at least one population of fibers comprises synthetic fibers and at least one population of fibers comprises natural fibers. 